The invention is a solar energy collector that produces electricity and heat using an optically transparent vessel containing photovoltaic cells and substantially filled with a non-conducting, optically transparent liquid, used for removing heat.
Devices that produce both electricity and heat from concentrated solar energy are known. However, such devices have been disclosed primarily using concentrated refracted solar energy, which are less effective in concentrating solar radiation. Concentrated refracted solar energy devices typically require a liquid with a high refractive index and a sun-tracker capable of orienting the device along two axes: the vertical orientation of the major axis, which is in effect rotation of the device about its minor axis; and the horizontal orientation of the minor axis, which is in effect rotation of the device about its major or longitudinal axis.
Concentrated refracted solar energy involves passing solar radiation through a lens to focus it and thus concentrate its effect. The present device does not use refracted or lens-concentrated solar energy. Rather, the present invention utilizes concentrated reflected solar energy. By so doing, the present invention can produce a higher concentration of sunlight with simple shapes, especially when a parabolic shape is used for the bottom exterior surface. Also, the present invention requires sun tracking only along a single axis, namely, rotation around its longitudinal axis. No complex two-axes tracking is required. Once the longitudinal axis of the present invention is aligned along the east-west direction, there is no need for large directional adjustment, only “fine tuning,” i.e., smaller and more precise adjustment is needed only for any seasonal change or slight misalignment of the device.
To produce a comparable concentration, a refractive device would need to a complex configuration with multiple lenses. With a simple design, the present invention improves efficiency while reducing the weight and quantity of material often associated with refractive devices. Overall, the present invention has advantages in lower-cost manufacture, ease of manufacture and broader application potential for backfitting to existing buildings.
The apparatus of the present invention concentrates sunlight via reflection, that is, the area of the sunlight used for the production of electricity is greatly reduced from the unconcentrated area of illumination by the sunlight. This reduced area of sunlight enables use of fewer solar cells to achieve the same electrical output for the solar energy impinging on the apparatus. Thus, it either enables use of fewer cells for the same electrical output, or for a comparable cost, it enables the use of high-efficiency photovoltaic cells, such as multi-junction solar cells. When a high-efficiency photovoltaic cell is utilized, the invention can translate to a more efficient device with a lower cost per unit of power.
The present invention combines a photovoltaic cell and a means for heat extraction in a unique arrangement to promote efficient operation of both means for extracting useful energy from solar radiation. It is known that a photovoltaic cell can produce electricity from sunlight and its efficiency can be maximized by maintaining the cell as close to ambient temperature as reasonably achievable in the presence of concentrated sunlight. The key to higher efficiency is to provide solar cell temperature regulation while at the same time enabling the extraction of the heat energy created by the sunlight. Therefore, the present invention enables a reflecting solar concentrator to be effective in producing electricity from one or more solar cells maintained near ambient temperatures and to easily extract the heat energy.
An alternative embodiment of the present invention employs solar tracking to rotate the apparatus so that solar radiation enters latitudinally perpendicular to the apparatus. Solar tracking is well known in the art. However, a specific means for achieving solar tracking is described for the present invention. Essentially, the vessel used in the apparatus is rotated about its longitudinal axis to achieve focusing. Two parallel solar cells on the inside top of the vessel are used to measure variation in relative radiation intensities and thereby send signals to rotate the vessel.